package com.lagou.sqlSession;

import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;

import java.lang.reflect.*;
import java.util.List;

public class DefaultSqlSession implements SqlSession {

    private Configuration configuration;

    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
    }

    @Override
    public <E> List<E> selectList(String statementid, Object... params) throws Exception {

        //将要去完成对simpleExecutor里的query方法的调用
        simpleExecutor simpleExecutor = new simpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementid);
        List<Object> list = simpleExecutor.query(configuration, mappedStatement, params);

        return (List<E>) list;
    }

    @Override
    public <T> T selectOne(String statementid, Object... params) throws Exception {
        List<Object> objects = selectList(statementid, params);
        if(objects.size()==1){
            return (T) objects.get(0);
        }else {
            throw new RuntimeException("查询结果为空或者返回结果过多");
        }
    }

    /**
     * 执行
     * */
    private Integer doExecute(String statementId, Object[] params) throws Exception {
        simpleExecutor simpleExecutor = new simpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        Integer rowsAffected = simpleExecutor.doExecute(configuration, mappedStatement, params);
        return rowsAffected;
    }

    @Override
    public <T> T getMapper(Class<?> mapperClass) {
        // 使用JDK动态代理来为Dao接口生成代理对象，并返回

        Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass}, new InvocationHandler() {

            /**
             * proxy就是newProxyInstance返回的对象
             * method是调用的方法
             * args是传入的参数（集合）
             *
             * */
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                // 底层都还是去执行JDBC代码 //根据不同情况，来调用selctList或者selectOne
                // 准备参数 1：statmentid :sql语句的唯一标识：namespace.id= 接口全限定名.方法名
                // 方法名：findAll
                String methodName = method.getName();
                //com.lagou.IUserDao
                String className = method.getDeclaringClass().getName();

                String statementId = className + "." + methodName;
                System.out.println("statementId:"+statementId);
                //com.lagou.IUserDao.findAll

                if ("findAll".equals(methodName)) {
                    // 准备参数2：params:args
                    // 获取被调用方法的返回值类型
                    Type genericReturnType = method.getGenericReturnType();
                    // 判断是否进行了 泛型类型参数化
                    //判断返回值是否使用了泛型，如果使用了泛型，就认为是返回的是列表
                    if (genericReturnType instanceof ParameterizedType) {
                        List<Object> objects = selectList(statementId, args);
                        return objects;
                    }
                    return selectOne(statementId, args);
                }

                if(args==null){
                    throw new Exception("传入dao的参数不能为空");
                }
                //取到要操作的参数类的名字 这里是User
                String paramTypeName = args[0].getClass().getSimpleName();

                //限制方法名
                if ("findOne".equals(methodName) ||
                        ("findBy"+paramTypeName).equals(methodName)) {
                    return selectOne(statementId, args);
                }
                if(("find"+paramTypeName+"s").equals(methodName)){
                    return selectList(statementId,args);
                }

                if (("add"+paramTypeName).equals(methodName)) {
                    return doExecute(statementId,args);
                }
                if (("update"+paramTypeName).equals(methodName)) {
                    return doExecute(statementId,args);
                }
                if (("delete"+paramTypeName).equals(methodName)) {
                    return doExecute(statementId,args);
                }
                //com.lagou.IUserDao.findByUser
                //com.lagou.IUserDao.addUser
                //com.lagou.IUserDao.updateUser
                //com.lagou.IUserDao.deleteUser
                throw new Exception("方法名不符合要求");
            }
        });

        return (T) proxyInstance;
    }
}
